The present invention relates to an apparatus for manufacturing a resin tube, and particularly to an apparatus suitable for manufacturing a resin tube of a large diameter.
In general, a conventional apparatus for manufacturing a resin tube of a large diameter comprises a plurality of rotatable forming rolls arranged on a hypothetical cylindrical surface, one end of each rotatable forming roll being supported by a support base like a cantilever and operably connected with a driving means. Each rotatable forming roll is slightly inclined with respect to the axis of the above hypothetical cylindrical surface. An extruder is positioned near the rotatable forming rolls, and an extruded resin ribbon is supplied to the forming rolls so that it is wound around the forming rolls with its side edges overlapped. With all of the forming rolls rotating simultaneously in the same direction, the resin ribbon is continuously conveyed toward the tip ends of the rotatable forming rolls while being formed into a tubular body with its edges overlapped. Since the resin ribbon is still sufficiently hot on the rotatable forming rolls, the partially overlapped resin ribbon is completely formed into a resin tube which is withdrawn continuously from the tip ends of the rotatable forming rolls.
However, the resin tube-forming apparatus of the above structure cannot produce resin tubes of different diameters because the rotatable forming rolls are arranged at a fixed diameter. Further, the rotatable forming rolls of a cantilever type are likely to undergo deformation during the tube forming operations, because cantilevers cannot remain straight under a large load imposed by a resin tube being formed thereon, which has a large diameter.